Communication apparatus and communication method utilizing multiple carrier waves for overcoming interference

ABSTRACT

There are included a transmission modulator ( 103 ) for impulse-modulating the data to be transmitted, thereby producing a subcarrier; a subcarrier control section for controlling the subcarrier to be utilized for communication, depending on the amount and significance of information and on the propagation condition of communication; and an antenna section ( 101 ) for radiating the subcarrier signal. This structure allows selection of a subcarrier suitable for information to be transmitted and for propagation environment, and hence allows a communication to be performed which exhibits a high flexibility and a high noise immunity. Thus, there can be provided a communication apparatus that can perform a high-quality, high-stability communication exhibiting an improved interfering immunity and that performs a flexible impulse communication.

This application is a U.S. national phase application of PCTinternational application PCT/JP03/10920.

TECHNICAL FIELD

The present invention is a technique for use in digital radiocommunication and, more particularly, relates to a technique for inimpulse communication.

BACKGROUND ART

Digital radio communication now occupies the important position in thefield of communication by virtue of the technological developmentthereof. In an attempt to pursue higher speed of communication, studyhas being put forward toward communication using impulse modulationscheme. Impulse modulation scheme involves the problem of being ready toundergo interference from other systems and hence become instable duringcommunication because of its occupation over a broadband frequency.Meanwhile, because of band occupation, there is a difficulty inmultiplexing a plurality of channels.

However, as means for solving this, there are those as described in U.S.Pat. No. 5,677,927, for example. FIG. 44 shows the conventionalcommunication apparatus described in U.S. Pat. No. 5,677,927.

In FIG. 44, a subcarrier generator & modulator 4401 generates amodulation subcarrier signal to be modulated with an information signal,and outputs the modulation subcarrier signal to a subcarrier timemodulator 4402. By the subcarrier time modulator 4402, an encoded timingsignal is modulated to generate a modulated encoded timing signal. Thetiming signal is radiated in the form of an electromagnetic pulse, at atransmission antenna 4404 through an output stage 4403.

With the above configuration, the communication apparatus in the priorart makes an impulse signal into channels by the simultaneous uses ofsubcarriers different in frequency or waveform. By using separatesubcarriers at individual channels, communication is made feasiblesimultaneously at a multiplicity of independent channels.

However, in the configuration of U.S. Pat. No. 5,677,927, becausecommunication is by a broad use of band on the impulse modulationscheme, there is a difficulty in avoiding against the system that issueshigh output signals in a part of the band, resulting in readiness toundergo influence.

Meanwhile, because the interval of subcarrier frequencies is great indistance (interval equal to or greater than 500 MHz), there is aconspicuous difference appearing in frequency-based radio wavepropagation characteristic. Namely, concerning the higher-frequencysubcarrier, there is limitation in the area for transmission as comparedto the lower-frequency subcarrier. Thus, there is greater effect ofshadowing. Besides, attenuation is high at around shields such as walls.This is the case from the fact that generally, at lower frequency band,communication is favorable with reduced circuit disconnections andbroader communication area while, at higher frequency band, circuitdisconnection is higher in rate and communication area is narrower.

These can be responsible for the followings.

Free space propagation loss: loss increases with increasing frequency.Narrowing communication area.

Transmission characteristic: loss of transmission through a shieldincreases with increase of frequency.

Diffraction effect: diffraction effect decreases and shadowing influenceincrease with increase of frequency.

Consequently, the communication system using impulse modulation schemehas the problem of the above conspicuous setbacks, as compared to thecommunication system in the prior art having a carrier interval ofapproximately several MHz to several tens MHz.

DISCLOSURE OF THE INVENTION

A communication apparatus according to the present invention, solvingthe foregoing problem, is allowed for suited communication by assigningtransmission subcarriers, depending upon communication informationsubstance (significance, control information or not), informationcapacity and communication quality required. This enables communicationshighly flexible and immune to noises.

Meanwhile, a communication apparatus comprises: a transmission modulatorfor impulse-modulating transmission data and generating subcarriers; acarrier control section for controlling the subcarriers for use incommunication depending upon information amount, significance andcommunication propagation condition; and an antenna section forradiating the subcarrier signals. This can select subcarriers suited fortransmission information and propagation environment, hence allowing forcommunications highly flexible and immune to noises.

Meanwhile, a communication apparatus according to the invention furthercomprises a reception modulator for detecting reception data andexamining a reception power on each subcarrier, to notify to thesubcarrier control section a permission/non-permission to use thesubcarrier, depending upon the reception power examined by the receptiondemodulator. This can dynamically change the subcarriers for use inchanging the communication environment, hence making possible to securestable communication quality.

Meanwhile, a communication apparatus according to the invention ischaracterized in that the carrier control section causes hopping on twoor more of the subcarriers.

Meanwhile, a communication apparatus according to the invention ischaracterized in that the carrier control section causes spread on twoor more of the subcarriers.

Meanwhile, a communication apparatus according to the invention ischaracterized in that the transmission modulator changes an on-frequencyallocation of the subcarriers according to communication condition.

Meanwhile, a communication apparatus according to the invention ischaracterized in that the transmission modulator assigns a narrower bandto the subcarrier having a lower center frequency and a broader band tothe subcarrier having a higher center frequency.

Meanwhile, a communication apparatus according to the invention furthercomprises a channel control section for selecting and controlling thesubcarrier for use on each channel, the channel control sectionperforming communication over two or more channels with different onesof the subcarriers.

Meanwhile, a communication apparatus according to the invention ischaracterized in that the channel control section performs communicationover two or more channels with a combination of different ones of thesubcarriers.

Meanwhile, a communication apparatus according to the invention ischaracterized in that carrier control section performs communication ofcontrol information by at least one of the subcarriers.

Meanwhile, a communication apparatus according to the invention ischaracterized in that the transmission modulator multiplexes togetherthe pieces of control information on two or more channels by use of anyone of time division multiplexing and code division multiplexing, in atleast one subcarrier of two or more of the subcarriers.

Meanwhile, a communication apparatus according to the invention ischaracterized in that the transmission modulator carries out frequencydivision duplex by use of two or more of the subcarriers.

Meanwhile, a communication apparatus according to the invention ischaracterized in that the transmission modulator carries out frequencydivision duplex by use of three or more of the subcarriers.

Meanwhile, a communication apparatus according to the invention ischaracterized in that the subcarrier with which the transmissionmodulator is to communicate the control information has a centerfrequency lower than a center frequency of the other subcarrier.

Meanwhile, a communication apparatus according to the invention ischaracterized in that the subcarrier with which the transmissionmodulator is to communicate the control information has a band narrowerthan a band of the other subcarrier.

Meanwhile, a communication apparatus according to the invention ischaracterized in that the transmission modulator divides one symbol intotwo or more of the subcarriers, thereby multiplexing two or morechannels.

Meanwhile, a communication apparatus according to the invention ischaracterized in that the transmission modulator causes frequencyhopping in one symbol by use of two or more of the subcarriers, tothereby multiplexing two or more channels.

Meanwhile, a communication apparatus according to the invention ischaracterized in that the transmission modulator causes encoding spreadof one symbol onto two or more of the subcarriers, to therebymultiplexing two or more channels.

Meanwhile, a communication apparatus according to the invention ischaracterized in that the transmission modulator causes spread of onesymbol onto two or more of the subcarriers and two or more chips,thereby multiplexing two or more channels.

Meanwhile, a communication apparatus according to the invention ischaracterized in that the antenna section comprises a plurality ofantenna elements. Consequently, because the antenna elements aresuperior in narrower band characteristic in respect of radiationcharacteristic and mechanical form, size reduction and performanceimprovement are facilitated.

Meanwhile, a communication apparatus according to the invention ischaracterized in that the antenna section has a frequency characteristicof a multi-band characteristic.

Meanwhile, a communication apparatus according to the invention ischaracterized in that the antenna elements are different in centerfrequency of frequency characteristic.

Meanwhile, a communication apparatus according to the invention ischaracterized in that the antenna elements have band characteristics notto overlap on a frequency axis.

Meanwhile, a communication apparatus according to the invention ischaracterized in that the antenna section receives radio wave on asubcarrier-by-subcarrier basis and outputs the subcarrier signal to thereception modulator.

Meanwhile, a communication apparatus according to the invention ischaracterized in that the antenna elements have frequencycharacteristics corresponding to the subcarriers and radiate subcarriertransmission signal as a radio wave.

Meanwhile, a communication apparatus according to the invention ischaracterized in that the reception demodulator has a compensationsection for detecting a characteristic of a signal sequence of eachsubcarrier from a known signal received from a communication partner andcompensating for the characteristic.

Meanwhile, a communication apparatus according to the invention ischaracterized in that the characteristic is a frequency characteristic.

Meanwhile, a communication apparatus according to the invention ischaracterized in that the characteristic is a time responsecharacteristic, the compensation section compensating for the timeresponse characteristic by a correlation signal of a correlator.

Meanwhile, a communication apparatus according to the invention ischaracterized in that the reception demodulator comprises a spread codestoring section for storing a spread code and extracting a spread codecorresponding to the subcarrier, and a dispread section for making aconvolution operation of the subcarrier signal and the spread codeextracted at the spread code storing section.

Meanwhile, a communication apparatus according to the invention ischaracterized in that the transmission demodulator comprises a spreadcode storing section for storing a spread code and extracting a spreadcode corresponding to the subcarrier, and a spread section for making adirect spread onto the subcarrier from the modulation signal dividedinto the subcarriers and the spread code extracted at the spread codestoring section.

Meanwhile, a communication apparatus according to the invention ischaracterized in that the reception demodulator comprises a switchsection for switching over by frequency hopping on the subcarrier, thecarrier control section carrying out the control in the switch section.

Meanwhile, a communication apparatus according to the invention ischaracterized in that the transmission demodulator comprises a switchsection for switching over by frequency hopping on the subcarrier, thecarrier control section carrying out the control in the switch section.

A communication method according to the present invention is acommunication method for impulse modulation communication using aplurality of subcarriers, the communication method comprising: a step ofmeasuring a reception power on every subcarrier in a non-signal state,in an initial state prior to starting a communication; and a step ofdetermining the reception power measured and selecting the subcarrierusable in communication. This can detect properness of a subcarrier,hence allowing for communication using only a subcarrier suited forcommunication.

Meanwhile, a communication method according to the present invention ischaracterized in that the determination is to use, in a latercommunication, the subcarrier having the reception power equal to orsmaller than a predetermined value. This can detect a subcarrier beinginfluenced of radio wave from the other, hence allowing forcommunications using only a subcarrier suited for communication.

Meanwhile, a communication method according to the present inventionfurther comprises a step of measuring a reception power on everysubcarrier of a received known signal at a start of communication; and astep of selecting the subcarrier having the measured reception powerequal to or greater than a predetermined value, as a subcarrier usablein communication. This can detect a subcarrier with which transmissiondata is not easy to propagate, hence allowing for communications usingonly a subcarrier suited for communication.

As described above, the present invention allows for a quality, stablecommunication immune to interfering waves.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a figure showing an arrangement of a communication systemaccording to embodiment 1 of the present invention.

FIG. 2 is a figure showing an arrangement of a communication apparatusaccording to embodiment 1 of the invention.

FIG. 3 is a figure showing a relationship between a band and asubcarrier according to embodiment 1 of the invention.

FIG. 4 is a figure showing an arrangement of a reception modulatoraccording to embodiment 1 of the invention.

FIG. 5 is a figure showing an arrangement of a transmission modulatoraccording to embodiment 1 of the invention.

FIG. 6 is a figure showing a frequency hopping pattern according toembodiment 4 of the invention.

FIG. 7 is a figure showing a multiplexing based on frequency hoppingaccording to embodiment 4 of the invention.

FIG. 8 is a figure showing a frequency hopping pattern according toembodiment 4 of the invention.

FIG. 9 is a figure showing an arrangement of a reception modulatorcorresponding to spread communication according to embodiment 3 of theinvention.

FIG. 10 is a figure showing an arrangement of a transmission modulatorcorresponding to spread communication according to embodiment 3 of theinvention.

FIG. 11 is a figure representing a subcarrier characteristic accordingto embodiment 1 of the invention.

FIG. 12 is a figure showing a relationship between a interfering waveand a subcarrier according to embodiment 1 of the invention.

FIG. 13A is a figure showing an impulse modulation signal superimposedby a interfering wave according to embodiment 1 of the invention.

FIGS. 13B and 13C are figures showing the subcarriers of an impulsemodulation wave according to embodiment 1 of the invention.

FIG. 14 is a figure showing an arrangement of a communication apparatusaccording to embodiment 1 of the invention.

FIG. 15 is a figure showing a relationship between a subcarrier and achannel according to embodiment 2 of the invention.

FIG. 16 is a figure showing a subcarrier signal waveform according toembodiment 2 of the invention.

FIG. 17 is a figure showing a relationship between a subcarrier and acode according to embodiment 3 of the invention.

FIG. 18 is a figure showing a code division multiplexing according toembodiment 3 of the invention.

FIG. 19 is a figure showing an arrangement of a communication systemaccording to embodiment 3 of the invention.

FIG. 20 is a figure showing a frequency allocation according toembodiment 5 of the invention.

FIG. 21 is a figure showing a frequency assignment according toembodiment 5 of the invention.

FIG. 22 is a figure showing a frequency assignment according toembodiment 5 of the invention.

FIG. 23 is a figure showing a procedure for frequency assignmentaccording to embodiment 5 of the invention.

FIG. 24 is a figure showing an initial procedure according to embodiment5 of the invention.

FIG. 25 is a figure showing an arrangement of a transmitter/receiverapparatus according to embodiment 5 of the invention.

FIG. 26 is a figure showing an arrangement of a transmitter/receiverapparatus according to embodiment 5 of the invention.

FIG. 27 is a figure showing a relationship between a subset and asubcarrier according to embodiment 8 of the invention.

FIG. 28 is a figure showing a relationship between a subset and asubcarrier according to embodiment 8 of the invention.

FIG. 29 is a figure showing a frequency hopping pattern according toembodiment 8 of the invention.

FIG. 30 is a figure showing a frequency hopping pattern according toembodiment 8 of the invention.

FIG. 31 is a figure showing an arrangement of a receiver apparatusaccording to embodiment 8 of the invention.

FIG. 32 is a figure showing a relationship between a filtercharacteristic and a subcarrier according to embodiment 5 of theinvention.

FIG. 33 is a figure showing the waveform of an impulse signal andreception signal according to embodiment 7 of the invention.

FIGS. 34A and 34B are figures showing the waveform of an impulse signaland reception signal according to embodiment 7 of the invention.

FIG. 35 is a figure showing the waveform of an impulse signal andreception signal according to embodiment 7 of the invention.

FIG. 36 is a figure showing the waveform of an impulse signal andreception signal according to embodiment 7 of the invention.

FIG. 37 is a figure showing the waveform of an impulse signal andreception signal according to embodiment 7 of the invention.

FIG. 38 is a figure showing an arrangement of a receiver apparatusaccording to embodiment 9 of the invention.

FIG. 39 is a figure showing a subcarrier signal waveform according toembodiment 9 of the invention.

FIG. 40 is a figure showing a transmitter apparatus and receiverapparatus according to embodiment 2 of the invention.

FIG. 41 is a flowchart showing a communication operation according toembodiment 5 of the invention.

FIG. 42 is a sequence chart showing a communication operation accordingto embodiment 5 of the invention.

FIG. 43 is a figure showing a filter characteristic possessed by afilter section according to embodiment 6 of the invention.

FIG. 44 is a figure showing an arrangement of a communication apparatusin the prior art.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereunder, embodiments of the present invention are explained by use ofthe drawings. Note that the constituent element having like function inthe figure is attached with like reference.

Embodiment 1

Using the figures, explanation is made on the invention (particularly indemodulation) that an impulse signal is divided into two or morebandwidths (subcarriers), the signals of which are to be used inimplementing communication. FIG. 1 is a diagram showing a communicationsystem using the conventional impulse modulation signal, wherein 150represents a transmitter apparatus and 151 a receiver apparatus. Thetransmitter apparatus 150 comprises an antenna section 101 and atransmission modulator 102 while the receiver apparatus 151 comprises anantenna section 101 and a reception demodulator 103. FIG. 2 is a diagramexplaining in detail the transmitter apparatus 150 and the receiverapparatus 151 shown in FIG. 1, thus configuring a transceiver apparatusas a combination of the transmitter apparatus 150 and the receiverapparatus 151 for the sake of convenience. The blocks corresponding toFIG. 1 are attached with the same references, hence to describe hereinthe different point only. 250 is a filter section for inputting a signaland divides it into a plurality of subcarrier signals narrower inbandwidth than the input signal. 102 is a reception demodulator forinputting a plurality of subcarrier divisional signals divided by thefilter section 250 to thereby receive and demodulate it, which isconfigured by a reception section 202 and a demodulator 203. 202 is areception section for power-amplifying the input reception signal andoutputting an amplified signal. 203 is a demodulator for inputting theamplified signal, to detect information from reception time, amplitudeand phase, etc., and output reception data. 103 is a transmissionmodulator for inputting, modulating and power-amplifying thetransmission data and outputting a subcarrier transmission signal, whichis configured by a modulator 204 and a transmission section 205. 204 isa modulator for impulse-modulating the input transmission data on apredetermined scheme and outputting a subcarrier modulation signal. 205is a transmission section for inputting and power-amplifying asubcarrier modulation signal and outputting a subcarrier-transmissionsignal. The signal outputted from the transmission section 205 isband-limited in its subcarriers by the filter section 250 so that amultiplexed transmission signal is supplied to the antenna section 101.The filter section 250 is formed by a plurality of filters 201 for bandlimitation. The filter section 250 has a pass characteristic assumablyconfigured as shown in FIG. 3. Namely, the plurality of filters 201 areto respectively limit different bands, and correspond to the subcarriersshown in FIG. 3.

Using a transmission apparatus 150 and reception apparatus 151 thusconfigured, explanation is made on a communication method of an impulsemodulation scheme. Incidentally, the transmission apparatus 150 is madeup by a transmission modulator 103, a filter section 250 and an antennasection 101. The reception apparatus 151 is constituted by an antennasection 101, a filter section 250 and a reception modulator 102.

The modulator 204 inputs transmission data, and impulse-modulates itaccording to a predetermined procedure. Impulse modulation is knownincluding pulse-position modulation that is to superimpose informationover pulse time interval, pulse-phase modulation that is to superimposeinformation over pulse phase, and pulse-amplitude modulation that is tosuperimpose information over pulse amplitude. In this manner, an impulsemodulation wave is generated corresponding to transmission data, tooutput a subcarrier modulation signals in an amount of a predeterminednumber of subcarriers. The subcarriers are attached with the samesymbol. The subcarrier modulation signals are inputted to thetransmission sections 205, to be output as power-amplified subcarriertransmission signals therefrom. The power-amplified subcarriertransmission signals are inputted to the filter section 250 andband-limited by the corresponding filters 201. The impulse modulationsignal has a feature having a much-broadened band because it is animpulse-natured signal. Consequently, there is a feature that, even whenpassed through a narrower-banded filter having a different centerfrequency, there exists a corresponding frequency component. Thus,output is obtainable in accordance with a filter. Namely, thetransmission signal outputted from the filter section 250 is such asignal as having a frequency characteristic shown in FIG. 3, in a statemultiplexed with a plurality of subcarrier signals 201 to 207. Thetransmission signal is supplied to the antenna section 101, to radiatean electromagnetic wave by the radiation characteristic thereof.

The electromagnetic wave thus radiated is received by the antennasection 101 of the reception apparatus 151, to output a receptionsignal. The reception signal is divided into subcarriers band-limited bythe filters 201 of the filter section 250, to be output as subcarrierdivisional signals. The filter section 250 has the same frequencycharacteristic as that band-limited by the transmission apparatus 150.The reception signal in the entire power is turned into subcarrierdivisional signals without substantial loss through the filters 210. Thesubcarrier divisional signals thus band-limited are power-amplified bythe reception sections 202 from which subcarrier reception signals areoutputted and those are supplied to the demodulator 203. The subcarrierreception signals inputted to the demodulator 203 are demodulatedaccording to pulse interval, amplitude and phase, and turned intoreception data.

Hereunder, the above operation is explained concretely.

Here, consider the case a certain disturbing wave is superimposed overthe input signal to the reception apparatus 151. FIG. 12 is a figureshowing a relationship between an impulse signal 1201 and a disturbingwave 1202, showing a state there exist one broadband signal 1201 (brokenline), seven subcarrier signals 1203 and one disturbing wave 1202. FIG.13A is a figure showing an impulse modulation signal superimposedthereon with a disturbing signal. FIG. 13B is a figure showingsubcarriers f4, f5 of the impulse modulation signal at that time.Meanwhile, FIG. 13C is a figure showing subcarriers f1 to f3, f6 and f7.Now consider here the case to communicate an impulse modulation signalremained as a broadband signal and the case to communicate it throughdivision into subcarriers as noted before, in order for comparison.

First of all, in the case a high-power disturbing wave is superimposedover a desired wave upon communicating an impulse modulation signalremained as a broadband signal as in the conventional, a high noisecomponent is added in the impulse portion (symbol in the impulsemodulation signal) or a signalless portion (symbol transition portion).In case this exceeds a predetermined level (saturation level),saturation occurs in the output signal thus resulting in signaldistortion. This manner is shown in FIG. 13A. As a result, duringdemodulating the impulse modulation signal, an impulse is detectederroneously due to the deviation. Otherwise, the accuracy of detectiondeteriorates conspicuously, to raise a serious problem in communicationquality. However, according to the communication apparatus of thepresent invention, in the case that similarly a disturbing wave issuperimposed over the communication signal divided into subcarriers,there is encountered a deterioration in the communication condition insubcarriers f4, f5 under heavy influence of the disturbing wave shown inFIG. 12, by the influence of the disturbing wave as shown in FIG. 13B.However, concerning the other subcarriers f1-f3, f6, f7, the disturbingwave is band-limited by the filter 201 as shown in FIG. 13C with aresult that the major part of disturbing wave power is removed to obtainhigh C/N. Generally, the disturbing wave, in few cases, has a power overa broad band, i.e. intense power frequently exists in a particular band.Therefore by providing a setting to allocate subcarriers over a broadband, the effect of relieving the influence is enhanced as noted above.For this reason, communications can be sustained in a favorable state bydemodulation with the use of subcarriers f1-f3, f6, f7 shown in FIG. 12.

Meanwhile, in the invention, subcarrier arrangement is established bythe filter section 250. Naturally, this can be designed freely.Disturbing waves frequently occur due to the use for communications orso by the other systems, and wherein it is possible to know in advance aband being used in the system in this manner. For this reason, by thedesign to previously avoid such disturbing wave bands by means of thefilter section 250, communication failure due to other systems can bereduced to the minimum.

In the above explanation, explanation was premised on that the samesubcarriers were formed for communication on both the transmissionapparatus 150 and the reception apparatus 151. However, the similareffect is available by effecting communications without formingsubcarriers (remained in broadband) on the transmission apparatus 150while performing demodulation by decomposition into subcarriers only onthe reception apparatus 151. Namely, where the transmission apparatus102 radiates an impulse modulation signal in the form of a broadbandsignal as it is while the demodulation apparatus 103 receives therelevant signal and demodulates it by division into subcarriers, theinfluence of a disturbing wave can be relieved similarly to theforegoing. In this case, the transmission apparatus does not require amechanism such as the filter section 250 for division into subcarriers,thus simplifying the arrangement. Furthermore, the loss based on thefilter section 250 is relieved thus enabling to configure an efficienttransmission apparatus 150. Meanwhile, this signifies that thesubcarrier reception scheme as the invention is applicable as areception apparatus of an impulse modulation communication system asconventionally used.

Furthermore, the subcarrier allocation must not be perfectly the same onthe transmission apparatus 150 and reception apparatus 151. Instead,communication is possible where there is an overlap in a given band.Namely, there is no necessity to maintain high the frequencycharacteristic accuracy of the filter sections 250 set up on each of thetransmission apparatus 150 and the reception apparatus 151. In thismanner, where there is a deviation in the frequency characteristic to beestablished by the filters 201 provided on the filter section 250,compensation is possible for those variations as errors. This approachis explained by use of FIGS. 4, 5 and 11.

FIG. 4 shows a further detail showing of the reception demodulator 102in FIG. 2. Here, f1-fn respectively represent subcarrier signals. 401 isa compensation section for compensating for an error (variation)occurring on each of the subcarrier-signal sequence and outputting asubcarrier compensated signal. 402 is an operation section for inputtingsubcarrier compensated signals and outputting an addition-operatedcarrier signal. 403 is a detection section for inputting a carriersignal and detecting an amplitude, phase and pulse interval of thepulse, to output corresponding reception data.

In the reception demodulator 102 configured as above, explanation ismade on a method of compensating for an error (variation) on each of thesubcarrier-based sequence. Here, explanation is based on the assumptionthat variation occurs mainly from frequency characteristics (of thefilters 201 arranged in the filter section 250). Incidentally,measurement assumably is previously made for the frequencycharacteristic of the filter section 250. Although the frequencycharacteristic is roughly classified as amplitude characteristic, delaycharacteristic and phase characteristic, the former two are taken on theassumption that phase characteristic is to be expressed by amplitudecharacteristic and delay characteristic. There is shown in FIG. 11 asignal waveform example of a subcarrier divisional signal in the case animpulse signal string is given to the antenna section 101 in FIG. 2. Ofthe subcarrier divisional signals in the figure, a subcarrier divisionalsignal f2 is shown as a reference signal. The broken line depicted oneach subcarrier divisional signal f1, f3 shows a reference signal f2,which is depicted in order for comparison. As shown in FIG. 11, providedthat, relative to reference signal f2, the subcarrier divisional signalf1 has an amplitude characteristic a1 (reference signal amplitude isnormalized 1) and a delay characteristic td1 while subcarrier divisionalsignal f3 has an amplitude characteristic a3 and a delay characteristictd3, the compensation section 401 corrects for the variation whilecontrolling the delay time and amplitude. Taking FIG. 11 as an example,the compensation section 401 corresponding to a subcarrier f1 sets adelay time at td+td1 and an amplitude gain at 1/a1 to thereby output asubcarrier compensation signal f1. Likewise in the subsequent, thecompensation section 402 corresponding to a subcarrier f2 sets a delaytime at td+0 and an amplitude gain at 1, while the compensation section402 corresponding to a subcarrier f3 sets a delay time at td−td2 and anamplitude gain at −1/a3, thereby respectively outputting subcarriercompensation signals. Noticing the pass characteristic of a subcarriersequence set at a broad frequency band, there can be considered a greatdifference between the pass characteristic of a subcarrier having thehighest center frequency and the pass characteristic represented bydelay time, phase rotation amount, pass gain, etc. of a subcarrierhaving the lowest center frequency. However, as explained before,because it is possible to synthesize a signal aligned in phase, delaytime and amplitude by compensating for characteristic variationoccurring on each subcarrier-based sequence and detecting the subcarriercompensation signal, higher quality of communication can be carried out.Meanwhile, in the transmission modulator 103 of the transmissionapparatus shown in FIG. 5, a compensation section 501 can be introducedin the modulator 204 similarly to the demodulator 203. Theprinciple/operation is similar to the compensation section 401 providedin the demodulator 203, and hence is omitted of explanation. In thismanner, higher quality of communication can be secured by compensatingfor subcarrier-based variations by use of the compensation section 501in the modulator 204.

Meanwhile, it can be considered to use a matched filter or the like inthe detection section 403. In this case, the function of thecompensation section 401 can be incorporated in the matched filtercharacteristic. It is the correlator that is known the most as a matchedfilter structure. The correlator is quite easy to be realized byadjusting a signal pattern used in correlation on asubcarrier-by-subcarrier basis. Likewise, in the waveform generationsection 502, the effect of the compensation section 501 can beincorporated by adjusting the pattern of a generating impulse pattern ona subcarrier-by-subcarrier basis.

The present invention is characterized in that an impulsive broadbandsignal is divided into subcarriers to be received and demodulated. Thisis not limited to the configuration shown in FIG. 2. As shown in FIG.14, it can be implemented on an arrangement in which the filter section250 and the reception section 202 and transmission section 205 areexchanged. In addition, similar effect is available even if there is nofilter section 250.

Meanwhile, although the antenna section 101 in FIGS. 1 and 2 can coverthe entire of subcarrier band by means of a single antenna element, aplurality of antenna elements may be provided corresponding topredetermined subcarriers. In the case of using the latter arrangement,there is conventionally a need to overlap the bands between antennas ormatch the characteristics in the overlapped bands. However, the presentinvention, because using the scheme of communications through subcarrierdivision, does not require to overlap between antenna-based bands ormatch the antenna-based characteristics. Meanwhile, generally, rather.than the antenna element having a broader band characteristic in theaspect of frequency, the antenna element having a narrower bandcharacteristic has many excellent points in terms of radiationcharacteristic (e.g. antenna gain), mechanical form, etc. From thisfact, size reduction and performance improvement is readily achieved onthe communication apparatus structuring an antenna section 101 with theuse of a plurality of antenna elements.

The present invention is characterized conspicuous in that the impulsemodulation signal is divided into subcarriers for the processing oftransmission and reception in the transmission apparatus 103 andreception apparatus 102 or only within the reception apparatus 102. Asfor the burden on the apparatus by the increase of sub-systems, theimpulse modulation communication apparatus does not require variouscircuits for processing of high-frequency waves (linear amplifiers,synthesizers, filters). This ban reduce by far the circuit scale ascompared to the increased circuit scale by the increase ofsubcarrier-based sequence. For this reason, the present invention can becarried out extremely easily, having a feature that great effect isobtainable while suppressing circuit burden.

Meanwhile, there is no need to provide the subcarriers with the sameoccupation band. Because the communication rate required is differentbetween the control channel for flow of control information and thetraffic channel for flow of data, broader band can be established to asubcarrier on a channel in which the greater communication rate issought. With such difference of bands, the difference in fractional bandcan be reduced by taking narrower the lower center frequency ofsubcarrier and broader the higher one of subcarrier.

Embodiment 2

With the use of figures, explanation is made on the invention that theimpulse modulation signal is divided into two or more bands(subcarriers) to thereby multiplex a plurality of channels of impulsemodulation communications by use of the subcarrier signals. FIG. 40 is adiagram showing an arrangement of a transmission apparatus 150 andreception apparatus 151 according to the present embodiment. In FIG. 40,there is a difference from that of embodiment 1 in that the transmissionmodulator 103 has further a channel control section 4001 while thereception demodulator 102 has further the channel control section 4001.The channel control section 4001 selects and controls the subcarriers tobe used on a channel-by-channel basis.

There is shown in FIG. 15 a correspondence between a communication and asubcarrier. As shown in FIG. 15, it is assumed that channel 1 is undercommunication by use of subcarriers f1, f3, f4, f6 while channel 2 isunder communication by use of subcarriers f2, f4, f5, f7. Herein,subcarrier setting is assumed similar in the transmission apparatus 150and in the reception apparatus 151.

Explanation is made on a method of multiplexing a plurality of channels,as to the communication system configured as in the above.

The subcarrier configuration of channel 1 and the subcarrierconfiguration of channel 2 are in the form of sharing subcarrier f4.There is shown in FIG. 16 a signal waveform on each subcarrier-basedsequence. As shown in the figure, subcarriers f1, f3, f6 and subcarriersf2, f5, f7 are occupied on the single channel without duplication.Consequently, impulse detection is possible without any problem.However, a subcarrier f4 is in a state in duplicated use by channel 1and channel 2. For this reason, when to detect an impulse, there is apossibility that it cannot be normally done due to interference.However, the reception apparatus 151, despite cannot normally detect animpulse on subcarrier f4, can normally detect an impulse phase,amplitude, time, etc. on the other carrier (f1, f3, f6 on channel 1; f2,f5, f7 on channel 2). Therefore, it can be understood that communicationis available only by those subcarriers. Moreover, in the case that thereis a constant deviation in symbol time between channel 1 and channel 2,it is possible to separate the impulse of subcarrier f4. By doing so,the subcarriers duplicated between the channels can be separated andutilized in demodulation on each channel. As a result, the total powerto be used per channel is improved and communication quality isexpectedly improved.

The above explained the method that the transmission apparatus 150 andthe reception apparatus 151 simultaneously make use of a plurality ofsubcarriers in the same combination. However, there is not always a needof agreement between the subcarriers to be established and transmittedby the transmission apparatus 150 and the subcarrier to be establishedand received by the reception apparatus 151. Normal communication isfeasible to implement provided that one or more subcarriers are sharedby the both apparatuses.

In this manner, channel capacity can be secured to a maximum extent byassigning one subcarrier to one channel. Meanwhile, by assigning all thesubcarriers to one channel, more stable communication can be providedbecause of securing a signal power per channel. In this manner, it ispossible to freely establish the number of subcarriers assigned to onechannel. This makes it possible to assign to the channel a smallernumber of subcarriers where much more channel capacity is needed, and agreater number of subcarriers where more stable communication isrequired.

Particularly, in the channel for conveying such important information ashaving a direct bearing upon system control and in such a channel ascomparatively attaching importance to communication capacity such as ofdata for use in application, more subcarriers can be assigned to theformer channel as compared to the latter channel, allowing forarchitecting an efficient system.

Meanwhile, the number of subcarriers in assignment may be changeddepending upon a communication capacity change, a propagation conditionchange or an interference wave condition change.

Furthermore, stable communication quality can be sustained by previouslymonitoring the subcarrier condition so that the subcarriers inassignment to the channel are dynamically changed in the event thatreception power is lowered, an interference wave signal is detected orinterference becomes problematic at between the channels.

Although the above explained the invention that the impulse modulationsignal is divided into two or more subcarriers to thereby multiplex aplurality of channels, a particular subcarrier is provided as a controlchannel exclusive for control information. By doing so, importantinformation is communicatable which is to be used in control or the likeindependently of the traffic channel.

Meanwhile, it is possible to simultaneously use a method of channelmultiplexing based on subcarrier division and multiplexing based on timedivision. For example, in the case of assigning a control channelexclusive for control information to one subcarrier, it is possible torealize it by time division multiplexing in order to share it by aplurality of terminals.

Embodiment 3

Explanation is made on the invention that the impulse modulation schemeis divided into two or more bands (subcarriers) so that communication iseffected by spreading codes to the subcarrier.

Embodiment 1 was explained to implement communication to attach the samesymbol on all the subcarriers assigned to one channel. However, in thecase a plurality of subcarriers are assigned to one channel, there is noneed to send the same symbols to all the subcarriers assigned. FIG. 17shows a relationship between a subcarrier and a code. The example shownin FIG. 17 shows a state that subcarrier f1-f7 are assigned to a certainchannel. Meanwhile, this figure represents that symbol set ss1 is usedin transmission for subcarriers f1, f3, f6 while symbol set ss2 is usedin transmission for subcarriers f2, f4, f5, f7.

In the below, explained is a communication system for transmission ofbinary data. This system includes at least two symbols (s1, s2).Provided that the relationship of symbols (e.g. s1←c1, s2←c2) to beassigned to transmitting codes (c1, c2) is assumed as a symbol set, itis possible in this case to consider a symbol set of (s1←c1, s2←c2) anda symbol set of (s2←c1, s1←c2) (the former is assumes as a symbol setss1, the latter is assumed as ss2). The transmission apparatus 150 obeysthe definition of symbol set, to generate and transmit a symbolcorresponding to a subcarrier from the transmission data. Conversely,the reception apparatus 151 obeys the same definition of symbol set, todetermine the reception data by means of a combination of symbolsreceived by each subcarrier. The conversion method of symbol set isexplained more concretely. Considering symbol c1 as +1 and code c2 as −1in the symbol set example referred before, it can be seen realizable if+1 is multiplied on the transmitting code in concerned with symbol setss1 and −1 on the transmitting code in concerned with symbol set ss2.Particularly, the multiplication between sets +1 and −1 is knownconfigured by exclusive OR. It is possible to extremely easily changedifferent symbol sets on a subcarrier-by-subcarrier basis.

Although the above explanation was on the assumption that there are twosymbols in the communication system to transmit binary data, this is notlimitative. It is satisfactory to provide the same modulation scheme(phase modulation, time modulation, amplitude modulation or the like) toeach symbol set. A plurality of modulation schemes can coexist on thesame channel; Meanwhile, practical application is possible with two ormore symbol sets.

In this manner, by allowing a plurality of modulation schemes tocoexist, a communication system with greater flexibility can bearchitected. Besides, the features different between modulation schemescan be well made use of.

Meanwhile, code division multiplexing can be effected by use of apredetermined subcarrier. Explanation is made by using FIG. 18. FIG. 18shows a state seven subcarriers (f1-f7) are assigned for code divisionmultiplexing. For simplicity, explanation is by use of the foregoingsymbol sets (ss1, ss2) and codes (c1=+1, c2=−1). Here, it is assumedthat symbol sets ss1, ss2 uses the same modulation scheme whereindefinition is made as (s1←c1, s2←c2) in ss1 while (s1←c2, s2←c1) in ss2.By the definition in this manner, consideration can be in a way as if itwere the same configuration as multiplication of a spread code in acarrier direction. Taking symbol set ss1 as +1 and ss2 as −1 andapplying those to FIG. 18, spread codes (assumed ss1-7) are given as inthe following:

channel 1: sc1={−1, +1, −1, +1, −1, +1, −1}

channel 2: sc2={+1, −1, −1, +1, +1, +1, −1}

channel 3: sc3={+1, +1, −1, −1, −1, −1, +1}

channel 4: sc4={+1, −1, +1, +1, −1, −1, +1}

channel 5: sc5={−1, +1, +1, −1, +1, −1, −1}

channel 6: sc6={−1, +1, −1, −1, +1, +1, +1}

channel 7: sc7={−1, −1, −1, +1, +1, +1, −1}.

Meanwhile, explanation is based on the assumption that the receptionapparatus 151 is to demodulate channel 1.

The transmission apparatus 150 makes a spreading in the carrierdirection by use of diffusion codes sc1-sc7 set on a chanel-by-chanelbasis, to transmit signal through multiplex by a predetermined number ofchannels (seven, here).

The method of spread is further explained by using FIGS. 9 and 10. FIGS.9 and 10 shows in greater detail the reception modulator 102 andtransmission modulator 103 of FIG. 2, wherein like reference is attachedto like function.

In FIG. 9, the reception demodulator 102 comprises a reception section202, a spread code storing section 901, a dispread section 902 and adetection section 403. 901 is a spread code storing section for storingand outputting a spread code set based on each channel, 902 is adispread section for outputting a dispread communication signalsynthesized by inputting a reception signal in an amount of the numberof subcarriers and multiplying thereon a spread code corresponding tothe subcarrier into synthesis.

In FIG. 10, the transmission modulator 103 comprises a transmissionsection 205, a spread code storing section 901, a spread section 1001and a waveform generation section 206. 1001 is a spread section forinputting a spread code and a waveform generated communication signaland multiplying a communication signal divided into subcarriers by thecorresponding spread code and outputting a spread communication signal.

The operation of the reception demodulator 102 and transmissionmodulator 103 configured as above is explained in detail.

When transmission data is inputted to the transmission modulator 103,the waveform generating section 206 generates a symbol waveformcorresponding to the data and outputs a communication signal. Thecommunication signal is divided into communication signals correspondingto the subcarriers inputted to the spread section 1001. Thecommunication signal divided is multiplied by a corresponding code ofthe spread code outputted from the spread code storing section 901, tothereby be output as a spread communication signal. The spreadcommunication signals are subjected to power-amplification and the likeby the corresponding transmission section and radiated through theantenna 101.

Meanwhile, the reception demodulator 102 inputs the spread receptionsignal of from the antenna 101. The spread reception signal is inputtedin an amount of the number of subcarriers, those of which arepower-amplified by the reception section 202. In the dispread section902, the spread reception signal power-amplified is multiplied by andsynthesized with a spread code corresponding to the subcarrier outputtedby the spread code storing section 901, to be output as a dispreadreception signal. This dispread reception signal is inputted to thedetection section 403, detected and output as reception data.

As in the above, the transmission modulator 103 makes a spreading on asubcarrier-by-subcarrier basis according to a spread code. Meanwhile,the reception demodulator 102 makes a reception by similarly carryingout a dispread, thus having a conspicuous feature enabling code divisionmultiplexing (CDM). Furthermore, privacy communication is feasible bymaking code setting in a manner not known by the third person.

Although the above explanation made the method of making a spreading inthe subcarrier direction, also possible are a method of making aspreading in a time direction or a method of making a spreading to bothsubcarrier and time. Meanwhile, it is possible to multiplex two or morechannels by making a spreading of one symbol onto two or moresubcarriers and two or more chips.

Embodiment 4

Explanation is made on the invention that the impulse modulation schemeis divided into two or more bands (subcarriers) so that communication iseffected by sequentially changing the subcarrier for use incommunication.

As for the reception demodulator 102 and the transmission modulator 103,those of FIGS. 9 and 10 are used in explanation similarly to embodiment3.

FIG. 6 is a figure explaining a hopping pattern that the subcarrier foruse in communication is changed in order. There is shown a subcarrierchange in a unit time by taking a time on abscissa and a frequency(subcarrier) on ordinate, showing that the hatched block is a subcarrierused in communication. Although the subcarrier changes with a constantperiod or according to a constant rule, this hopping pattern is sharedby the transmission end and reception end.

The shared hopping pattern is stored in the spread code storing section901 shown in FIGS. 9 and 10, wherein storage is with spread codes of +1,0 instead of +1, −1.

By the above configuration, the transmission modulator 103 transmits acommunication signal while changing the subcarrier in time. On the otherhand, the reception demodulator 102 is to change the hopping pattern intime, thereby selecting and receiving a subcarrier which thetransmission modulator 103 is using in communication. This enables tocorrectly receive data.

The above made an explanation on the example of communication usingmerely one subcarrier, with the method of which reception power ispossibly insufficient. For this reason, effective is a method ofsimultaneously using a plurality of carriers in order to supplement thereception power at the reception demodulator 102. This is explainedbelow by using FIG. 8.

FIG. 8 is a figure showing a hopping pattern when a plurality ofcarriers are used simultaneously. Design is made to use four subcarriersin one unit time, providing four times the reception power at thereception demodulator 102. The operation of the transmission modulator103 and reception demodulator 102, during communication, is the same asthe foregoing explanation. However, the hopping pattern stored in thespread code storing section 901 has numbers +1 and 0 only (one +1 andsix 0s in the former example, and four +1s and three 0s in the latterexample).

By adjusting the number of subcarriers for use in communication as inthe above manner, stable communication is made feasible. Meanwhile, bychanging the number of subcarriers in time, subcarriers can be givensmaller in the number in well communication condition while subcarriersbe given greater in the number in worse cases.

Although the above made an explanation as to communication with onechannel, a plurality of channels can be multiplexed similarly toembodiment 3.

Explanation is made below on a method of multiplexing a plurality ofchannels, by using FIG. 7.

FIG. 7 shows a state that two channels are multiplexed by frequencyhopping. Channel 1 and channel 2 shown in the figure make communicationswith using respective ones of subcarriers in unit time. The number ofsubcarriers per unit time can be changed on a channel or time basis.

By the above, a plurality of channels can be multiplexed to enablecommunication.

Embodiment 5

In the system shown in FIG. 19, explanation is made on a technique forrealizing frequency division duplex (FDD) with use of subcarriers.

FIG. 19 shows a figure showing a system configuration comprising acommunication apparatus having a bi-directional communication function.Although the figure takes a symmetric system as an example, it issatisfactory to use such an asymmetric system as 1-to-N. Meanwhile, forexplanation, communication from a communication apparatus 1950 to acommunication apparatus 1951 is explained as downlink whilecommunication from a communication apparatus 1951 to a communicationapparatus 1950 is as uplink, those communication directions are not tolimit the substance of the present technique.

For example, FIG. 20 shows a subcarrier on-frequency allocation. Thisshows a manner of coexistence of uplink subcarriers and downlinksubcarriers, showing a manner that frequency division duplex can becarried out without problem because channel orthogonality is held by thesubcarriers. Where to make a communication with one carrier without theuse of subcarriers, there is a need to carry out it with time division.In this case, control is required not to cause time overlap. Withfrequency division, time division control becomes unnecessary. Hence,realization is possible with simple configuration.

FIG. 25 is a showing of the communication terminals 1950, 1951 ingreater detail. The communication terminal 1950, 1951 comprises areception demodulator 102, a transmission modulator 103 and a carriercontrol section 2503. The reception demodulator 102 comprises areception section 202, a switch section 2501 and a detection section203, to input two or more subcarrier signals f1 to fn, input a carriercontrol signal 2510 and detect and output a signal of the correspondingcarrier. The transmission modulator 103 comprises a waveform generatingsection 206, a switch section 2501 and a transmission section 205, toinput transmission data 2513 and a carrier control signal 2511 andgenerates an impulse string corresponding thereto, thus outputting animpulse signal to the corresponding carrier. The carrier control section2503 inputs control information 2514 and control data 2515 of from thereception demodulator 102, and outputs carrier control signals 2510,2511 depending upon a carrier assignment sequence.

Explanation is made on a communication method for carrying out frequencydivision duplex by use of the communication terminals 1950, 1951configured as above.

FIG. 22 shows a frequency assignment sequence, showing the steps ofmanagement such as assignment/reallocation of a plurality ofsubcarriers. Meanwhile, FIG. 24 shows a sequence for initial settingFIG. 41 is a flowchart showing a communication operation of the presentembodiment.

(Session 1) At first, in both the communication terminals 1950, 1951,the carrier control section 2503 sets a subcarrier for use incommunication to an initial value, according to control information2514. It is possible to consider, as the initial value, setting forassignable subcarrier all usable, setting usable assignable subcarriersexcepting a predetermined particular subcarrier, and the like. Thesignal corresponding to a subcarrier selected in this manner isoutputted to the switch section 2501 of the reception demodulator 102and transmission modulator 103, thus determining switch status (stepS4101).

Next, the signal received by the reception section 202 is inputted tothe detection section 203 through the switch section 2501. The detectionsection 203 detects subcarrier-based reception power and outputs aresult thereof as control data 2515 to the carrier control section 2503.The carrier control section 2503 records as communication-not-permittedcarrier a carrier having reception power exceeding a predetermined value(step S4102).

(Session 2 a) Next, in the communication terminal 1950, a predeterminedinitial signal is inputted as transmission data 2513, to generate acorresponding impulse signal through the waveform generating section206. This impulse signal is selected of subcarriers by the switchsection 2501 and outputted through the transmission section 205 (step4103).

Meanwhile, in the communication terminal 1951, the initial signal isreceived by the reception modulator 102 and inputted to the detectionsection 203 through the switch section 2501. In the detection section203, the initial signal as a known signal is used to carry out timesynchronization, subcarrier-based characteristic compensation settingand subcarrier quality detection. In the case the quality does no reacha predetermined value, the corresponding carrier is recorded asincompetence for data communication (step 4104).

(Session 2 b) Next, the operations of communication terminals 1950 and1951 are exchanged to respectively make operations of steps S4103,S4104.

The above operation enables to know a use state of a frequency resourcefor use in communication. Namely, interfering immunity of from externalsystem can be detected by session 1 and mutual-communication propagationcharacteristic can be by session 2 a/ 2 b.

Meanwhile, by including the terminal ID codes respectively included inthe communication terminals 1950, 1951 and subcarrier informationcorresponding to apparatuses in the initial signal to be exchanged insession 2 a/session 2 b, the subcarrier usable in communication can beshared by the both terminals.

Depending upon the above detection result and terminal information, thecarrier control section 2503 of the communication terminal 1950, 1951determines an uplink/downlink subcarrier according to a predeterminedrule. Thus, the reception modulator 102 of the communication terminal1950 is set up with an uplink subcarrier while the transmissionmodulator 103 is set up with a downlink subcarrier. In the othercommunication terminal 1951, the reception demodulator 102 is set upwith a downlink subcarrier while the transmission modulator 103 is setupwith an uplink subcarrier. In a system for symmetric communication,because there is no distinction between uplink and downlink (symmetric),similar operation is enabled by temporarily setting uplink and downlinkby a predetermined method (ID code magnitude).

(Session 3 a) Next, the communication terminal 1950 transmits adetermined downlink subcarrier. When the communication terminal 1951receives the downlink subcarrier received, the information is inputtedas control data 2515 from the detection section 203 to the carriercontrol section 2503. According to the control data 2515, set is thestatus of switch 2501 in the reception demodulator 102 (step S4105).

(Session 3 b) The communication terminal 1951 transmits determineduplink subcarrier information similarly to session 3 a. When thecommunication terminal 1950 receives the uplink subcarrier information,the information is inputted as control data 2515 from the detectionsection 203 to the carrier control section 2503. According to thecontrol information, set is the status of switch section 2501 in thereception modulator 102 (step S4105).

Next, after the communications in sessions 3 a and 3 b, the bothcommunication terminals sets the switch section 2501 in the transmissionmodulator 103, to downlink subcarrier in the communication terminal 1950and to uplink subcarrier in the communication terminal 1951, thuscompleting the setting of uplink/downlink subcarriers (step S4106).

(Session 5) The communication terminals 1950, 1951 start a communicationby use of the uplink subcarrier and downlink subcarrier (step S4107).

The above procedure enables subcarrier assignment. Because such aprocedure if conducted enables to previously examine the interferencecharacteristic with other systems prior to communication start, it iseasy to grasp a subcarrier usable in communication. Simultaneouslytherewith, because subcarrier communication condition is examinedbetween the communication terminals, it is easy to grasp a propagationstatus formed between the communication terminals. Finally, it ispossible to easily select a subcarrier suited for communication.

As for subcarrier assignment methods, various methods are to beconsidered. This is explained using FIG. 21. The subcarrier assigned inthe above initial state, when requiring a downlink (or uplink) band, canadd and utilize free subcarriers f3, f6, as shown in communication state(1). By doing so, system flexibility can be secured by changingsubcarrier utilization ratio in accordance with communication band.Further, because of no use of unnecessary band, power-savedcommunication is feasible that is high infrequency utilization ratio.Meanwhile, as shown in communication state (2), where uplink (ordownlink) requires the maximum band, a communication system high infrequency utilization efficiency and maximum transmission capability canbe architected by implementing communications by utilization of all thesubcarriers determined usable in the subcarrier status examinationconducted in the initial operation.

Meanwhile, as shown in communication state (3), when to desirably sendat the maximum transmission capability, it is effective to leave at lestone subcarrier free as out of use in the uplink or downlink. This makesit possible to use the out-of-use subcarrier in exchanging controlsignals, exchanging resend information or the like, thus enablinghigher-leveled control/quality management. Furthermore, as shown incommunication state (4), there is a feature that control is made simpleby allocating the subcarriers for assignment in the uplink/downlinkaccording to a given rule. At this time, the rule can be considered torandomly assign the subcarrier numbers, to be assigned in the higher (orlower) order on the frequency axis, on the frequency axis thereby makingan assignment in the order of the subcarrier number.

Although the method of band assignment was explained in the above, bandassignment sequence is next explained by using FIGS. 22 and 42.

FIG. 42 is a sequence chart showing a communication operation accordingto the present embodiment.

In the initial state in FIG. 22, there is shown a state that subcarriersare assigned to uplink/down link by the initial operation (step S4201)shown at step S4101 to S4106.

Next, the communication terminal 1951, when requiring a transmissioncapacity, sends an uplink signal including a band request signal (stepS4202).

Next, the communication terminal 1950, when receiving the band requestsignal, examines that a subcarrier requested is not in use. Then, itsends a downlink signal including a band-use permission signal and setsthe corresponding subcarrier to a reception state (step S4203).

Next, the communication terminal 1951, when receiving the band-usepermission signal, sets the permitted subcarrier to a transmission stateand starts a communication (step S4204).

Likewise, the transmission terminal 1950, when requiring a transmissioncapacity, sends a downlink signal including a band request signal (stepS4205).

Next, the communication terminal 1951 receives the band request signaland conducts an interference examination on the subcarrier requested.Confirming an interference of subcarriers as a result of examination,the communication terminal 1951 determines whether or not to release it.In the case to release, the interfering subcarrier is released andsimultaneously a band-use permission signal included in an uplink signalis sent. Conversely, in the case not to release it, a band-usepermission signal is generated in a manner to permit a part of bandonly, or in a manner to reject whole band required, to send an uplinksignal including it (step S4206).

Next, the communication terminal 1950, when receiving the bandpermission signal, makes a switching over to the correspondingsubcarrier and starts a communication (step S4207). In the case the bandis rejected and the communication capacity is insufficient, a bandrequest signal is again sent after a lapse of a predetermined time (stepS4208).

Concerning the band request signal and band-use permission signalexplained above, it is possible to exchange these signals with adesignation of a subcarrier for increase and decrease. By providingcontrol in this manner, a flexible system can be architected.

On the other hand, where subcarrier control is according to a givenrule, the band request signal and the band-use permission signal can beexchanged solely to increase/decrease the number of subcarriers. By thusproviding control, flexible system control is available with a reducedamount of information. Meanwhile, the band request signal can be addedtherein with use information. Namely, by including in a band requestsignal a use as numerical information about a degree of significance,urgent degree or scheduled use time or the like, a higher level ofassignment operation is feasible.

Although band assignment procedure was explained in the above, there isa resend method as one technique for improving communication quality.Although this procedure can be grasped similarly, it may be a separateprocess if considering it as temporary use. A procedure rendered as aseparate one is shown in the below.

The communication apparatus 1950, when confirming a trouble occurrencein transmission over the uplink, sends a downlink signal including aresend request signal 2210. The communication terminal 1951, whendetecting a resend request signal 2210 out of the reception signal,looks for a free band and outputs a resend notification signalrepresentative of resending by use of an out-of-use subcarrier. Thecommunication terminal 1950, when receiving the resend notificationsignal 2211, sets the corresponding subcarrier into that for receptionand starts to receive resend information. The communication terminal1951, after a lapse of a predetermined time, puts the resend information2212 onto the subcarrier designated before and carry out communication.After sending the resend information, it releases the subcarrier usedfor the same and returns to the former communication state.

Meanwhile, the communication terminal 1951, in the case there is no freeband upon detecting a resend request signal 2210, determines to selectas a subcarrier anyone of a subcarrier being used in the uplink or asubcarrier being used in the downlink, and sends the information thereoftogether with a resend notification signal 2211. The communicationterminal 1950, when receiving the resend notification signal 2211,detects whether or not there is a necessity to release the subcarrierfor downlink. In the case there is a necessity of release, thesubcarrier is released and the same is set for reception. Thecommunication terminal 1951, after a lapse of a predetermined time fromsending of the resend notification signal 221, sends resend informationby use of a corresponding subcarrier.

Concerning the resend request signal and resend notification signalexplained in the above, exchange is possible by designating a particularsubcarrier for resending. By providing control in this manner, aflexible system can be archtected. Meanwhile, in the case thatsubcarrier assignment for resend information is previously set, signalexchange is possible without specifying a subcarrier in the resendrequest signal or resend notification signal. By providing control inthis manner, flexible system control is possible with a reduced amountof information. Meanwhile, the resend request signal can be addedtherein with information as a use thereof. Namely, higher level ofassignment operation is made possible by including, in the resendrequest signal, a significance and emergency of resending or a degree ofscheduled use time as numeral information.

In the above, explained was the method of implementing a communicationby assigning an uplink/downlink subcarrier. Generally, the communicationsystem requires, separately from information for transmission,information for use in managing and control of those. It is possible toset such a subcarrier exclusive for control signals to be issued betweencommunication terminals or from another terminal, separately from theuplink/downlink.

Explanation is made on session 0, session 4 and session 5 in FIG. 24.

(Session 0) The communication terminals 1950, 1951 notify to each othera communication start status by use of a control signal, as apreparation prior to the initial state (1). The communication terminal1950 transmits a control signal representative of a communication startby the use of predetermined one or more subcarriers. The communicationterminal 1951 receiving it makes a preparation for the initial state(1).

(Session 4) The communication terminals 1950,1951 notify a fact ofsubcarrier assignment completion, by the use of the control signal. Thecommunication terminal 1950 notifies completion of the assignment of asubcarrier for use in communication, thus making a control such that thesubsequent communication is carried out by use of the assignedsubcarrier.

(session 5) The communication terminals 1950, 1951 notify a negotiationcompletion to each other. This is assigned with at least threesubcarriers for uplink, downlink, and control, to carry out acommunication between the communication terminals 1950, 1951.

The above procedure enables subcarrier assignment. By thus assigningsubcarriers for control, control information can be exchanged withouthaving an effect upon information conveyance of from another system inthe course of communication or upon transmission capacity at between thecommunication terminals 1950. 1951. This enables to architect a stablecommunication system. Particularly, where constituted by three or morecommunication terminals, subcarrier request/assignment can be effectedin a unitary fashion, hence enabling to easily architect an efficienthigh-performance communication system.

Meanwhile, subcarrier f4 can be assigned as a subcarrier for control.The operation in this case is explained by using FIG. 23.

In FIG. 23, this is the case similar to the foregoing embodiment exceptin that a request signal and permission signal are exchanged only bysubcarrier f4. Due to this, control information can be exchanged at alltimes, hence eliminating the prohibition against request issuance untilbecoming free of a subcarrier.

Incidentally, the present embodiment explained the operation on theapparatus shown in FIG. 25. However, in case the sub-block concept asshown in embodiment 8 or subcarriers made be handled as independentsignals separated in frequency by a filter, the switch section 2501 isrendered unnecessary thus enabling practical application with a simplestructure as shown in FIG. 26.

Embodiment 6

FIG. 43 is a figure showing a subcarrier band characteristic in thepresent embodiment. This band characteristic is realized by themodulator 204 of the transmission apparatus and demodulator of thereception apparatus in the present embodiment. Excepting this point,this has the same configuration as embodiment 1.

In FIG. 43, the subcarrier having a higher center frequency is assignedwith a broader band. This is because the subcarrier having a highfrequency is limited in communication area and hence can be repeatedlyutilized as compared to the lower subcarrier. Besides, because of highattenuation by the shields, it is characterized in that there is lessleakage to the adjacent room (partition, building). In view of thisfact, it can be considered efficient to assign a broadband. Namely, byassigning a broader band to a subcarrier having a high center frequencyto thereby practicing higher-speed of communication, it is possible toeasily architect a system high in (frequency, space) utilizationefficiency.

In the case of information to be shared by some apparatuses such ascontrol signals, system stability can be improved rather by keepingpropagation condition well and selecting a subcarrier having a broadercommunication area. Namely, by assigning control information to asubcarrier lower in center frequency, a stable communication system canbe provided. Meanwhile, in the lower frequency band, there is a highpossibility that it is a frequency band to be used by other systems.(This is because it is a general practice to determine the frequencybands for use by a system in the order of from lower frequency.) Inconsideration of this, it is preferred to establish subcarriers inaccordance with system's use (i.e. taking account of free channels)instead of setting control information to a subcarrier the lowest incenter frequency.

As described above, a low-frequency subcarrier is assigned forcommunication requiring circuit quality, e.g. important information,control information and information transmission requiring communicationquality. For the other of communication, higher-frequency subcarriersare assigned. This can easily provides the optimal allocation. Astouched also in embodiment 1, by assigning a broader band to asubcarrier having a higher center frequency, higher-speed of broadbandcommunication can be realized with the subcarrier.

Meanwhile, control information can be communicated by frequency hopping.This is because, where there are subcarriers stable in communicationenvironment, there are increasing cases to enhance quality rather intransmission by a particular subcarrier. Furthermore, it is possible touse, in information, direct sequence technique in preparatory for anunforeseen event (e.g. sudden interfering signal issuance by anothersystem (or apparatus)). Furthermore, the control signal frequently hasinformation to be shared by some apparatuses. By multiplexing those bycode division multiplexing or time division multiplexing, some controlsignals can be stably exchanged by the same subcarrier. In the othersubcarriers than that used for the control signals, it can be consideredto use frequency hopping or assign a given subcarrier in compliance withinformation kind. By thus making direct sequence communication by atleast one subcarrier while carrying out frequency hopping communicationby the remaining subcarriers, a flexible high-level communication systemcan be architected. Meanwhile, it is preferred, in view of the nature ofcontrol signal, to fixingly assign a control signal to one subcarrierand apply, to the subcarrier, spread (direct sequence) in timedirection. This can architect a flexible stable communication system.

Although the above explained the event that frequency level appears as adifference in propagation characteristic, consideration may be made tothe ratio of band to center frequency of a subcarrier, i.e. relationshipin fractional band. For example, this includes that the filter having alarge specific band is difficult to design or realize.

Meanwhile, even in the communication within the same space, theinfluence of multipath is quite different from subcarrier to subcarrierbecause of large frequency spacing. For this reason, in the initialstage of communication, it is possible to prevent against deteriorationin communication quality by taking measures depending upon the influenceof multipath including (1) reducing the communication capacity of angreatly influential subcarrier, (2) correcting errors more definitely,(3) not used in communication. In these settings, by examining of andadapting to the influence of multipath during performing communicationbesides in the communication initial stage, adaptation is possible moresuitably to communication environment. This is similarly true for theinfluence upon a communication signal of from another system besides theinfluence of multipath.

Embodiment 7

Explanation is made on a method for architecting a flexiblecommunication system by varying a subcarrier band or varying theredundancy of data, in a system for communicating an impulse modulationsignal by use of subcarriers.

Embodiment 4 explained the technique for carry out frequency hoppingbased on each subcarrier. The frequency hopping technique can reduce thesymbol rate on one subcarrier, making it possible to relieve the effectof multipath.

However, the space where electromagnetic waves propagate is generallyconstituted with some different propagation paths based on reflection,diffraction, transmission and the like. The difference in path lengthdue to the difference of propagation path appears in the form of adifference in delay amount. It is expressed in delay dispersion by useof the delay time and attenuation amount. Because a reception signal isgiven as a synthetic result of delay dispersion and transmissionwaveform, different reception waveforms are observed by a propagationspace formed between transmission/reception terminals.

FIGS. 33 to 36 show signal waveform figures. FIG. 33 shows arelationship of a delay wave caused by the characteristic (delaydispersion) of a space where a transmission waveform (impulse signal)propagates and a reception wave as a synthesis thereof. As can be seenfrom the figure, it can be understood that an impulse signal having twopeaks, if added with a delay dispersion characteristic, changes into asignal having a number of local peaks.

FIGS. 34A and 34B show relationships where an impulse string is inputtedto the signal waveform of FIG. 33. The signal waveform of FIG. 34A andthe signal waveform of FIG. 34B respectively depict reception waveswhere impulse interval (symbol rate) is given tsymbol_A and tsymbol_B(where tsymbol_A<tsymbol_B), respectively depicting, withsuperimposition, to see a relationship of a single-impulsed receptionwave. As can be seen from the figure, in the case impulse interval issmaller than the maximum delay amount (tdelay) of delay dispersion, thereception waveform has an interference at between single-impulsesignals, to turn into a complicated waveform difficult to demodulate.Meanwhile, in the case impulse interval is longer than the maximum delayamount, the reception waveform is a combination of single-impulsedsignals. This can be understood demodulatable.

As in the above, it can be seen that a stable communication system canbe architected by changing the symbol rate by depending upon a delaydispersion formed in a propagation space by the transmission terminal.Here, the method for the transmission terminal to determine a delaydispersion can be a method of calculation/estimation by use of areception signal of from the opposite of communication, a method ofconveying a status of a delay dispersion calculated by the opposite ofcommunication onto the transmission terminal, and so on.

FIG. 35 shows a relationship between a delay dispersion and a delay waveand reception wave where the impulse width (tw) of a transmissionwaveform (impulse signal) is increased. Of the transmission waveform,the signal in the case with a short impulse width (the same condition asFIG. 33) is shown by a dotted line. In the case of long setting relativeto a delay difference (tdd) and maximum delay amount (tdelay) of delaydispersion, it can be seen that, if observing a signal waveform of thereception wave, the number of local peaks is greatly decreased ascompared to that of FIG. 33.

FIG. 36 is a depiction of a signal waveform relative to an impulsestring similarly to FIG. 34A or FIG. 34B. As mentioned above, becausethe waveform of the reception wave is approximated to an impulse form bysetting the impulse width (tw) long and further taking the impulseinterval (tsymbol) long, demodulation operation can be simplified, i.e.stable communication is made possible.

As explained above, by increasing and decreasing the impulse interval orimpulse width by utilization of the present embodiment, stablecommunication is made possible.

Although explained here was to control the impulse width, this issimilar for a pulse shaped (or band limited) signal if considering it byreplacing the envelope width with an impulse width. The impulse signal(A) in FIG. 37 shows a single-pulse signal waveform while the impulsesignal (B) shows a pulse-shaped signal waveform. By controlling theimpulse width (tw) of the signal waveform shown in the figure, it ispossible to relieve the influence of delay dispersion as noted above.

Meanwhile, controlling the impulse wave results in a change of signalband. Namely, signal band is narrowed by increasing the impulse widthwhile signal band is broadened by decreasing it. For example, a constant(e.g. 500 MHz) or higher band is required to utilize in communicationknown as the UWB (ultra wideband) system. In such a case, limitation canbe provided in the control range of impulse width.

Embodiment 8

Explanation is made on a technique of implementing communication withtwo or more subsets by using a certain number of subcarriers as asubset, in a system for communicating an impulse modulation signal byusing subcarriers.

In FIGS. 27 and 28, there is shown an on-frequency allocation ofsubcarriers f1-f12. Here, f1-f4/f5-f8/f9-f12 are considered respectiveone sets, which are assumed as subsets 1-3. By thus introducing aconcept of subset, the communication system using subcarriers so farshown in the other embodiment can be grasped as a system having thoseallocated in the number of subsets. Here, because the number ofsubcarriers included in the subset can be reduced to a proper number, itis possible to easily carry out subcarrier management/control.

Furthermore, by matching subset frequency allocation with filtercharacteristic such that the frequency characteristic of the filter 201(or antenna 101) in the input section shown in FIG. 2 is shown as afilter characteristic (dotted line) in FIG. 27, interference iseliminated from between the subsets. Accordingly, the foregoingsubset-based communication can be carried out mutually independently. Inthe case there are two or more subsets (assumed n here), communicationsystems apparently n in the number are allowed for communicationindependently. From this fact, by introducing the concept of subset, asystem can be architected with configuration quite simple and high inefficiency.

However, in the case of a communication system using an impulsemodulation signal, there can be considered a case that the filterscorresponding to subcarriers are not used because of separating thesubcarriers in order for simplifying the communication system.Meanwhile, even where providing filters, one filter is provided or sofor a base-band signal obtained by multiplying the reception signal by asignal having a subcarrier center frequency because of attachingimportance to simplicity and response characteristic.

FIG. 32 shows a case that the filter characteristic is not separated ona subset-by-subset basis. In such a case, because signal separation isnot made between the subsets, the subset singly cannot be operatedindependently. Namely, signal separation is not made between onesubcarrier and another subcarrier as in subcarriers f3 to f6, thesubcarriers are influenced in their mutual communication states. Forthis reason, by providing a filter characteristic corresponded at leastto the subsets, signal separation is achieved at between the subsetsthus enabling to independently operate the subsets.

FIG. 31 takes an arrangement that frequency conversion is made on thereception signal of subcarriers f1-fn frequency-allocated with thesubset by the same variable clock in a frequency conversion section3101, whose signals are added (or switched over) into a signal to bedetected by one detection section 203. If explaining it by using FIG.27, in the case of agreement between the f1 filter characteristic inFIG. 31 and the subset, because the subsets are already signal-dividedin frequency, there is no mutual interference between subset f1 andsubset f2-fn. Accordingly, the detection section can be configured inthe small number (one in FIG. 31). Namely, in FIG. 2, by making thefilter characteristic of the filter 201 singly or in combination agreewith the frequency characteristic given by the subset, the abovereception apparatus can be configured. Here, because the filtercharacteristic corresponding to the subset is extremely broad in bandand sufficiently high in response speed and the number of subsets aresmall as compared to the number of the subcarriers, it is possible toreduce the lower in simplicity due to the provision of filtercharacteristic and lower in response speed due to the filter, asmentioned above.

Here, the filter characteristic provided in the reception apparatus maybe any of from an antenna frequency characteristic to a frequencycharacteristic as a filter element, and an amplifier frequencycharacteristic. Particularly, the use of filter characteristic also asan antenna frequency characteristic greatly contributes to antenna sizereduction and characteristic improvement. Furthermore, by using arecently developed multimode antenna having a plurality of frequencycharacteristics, the antenna can be further reduced in size.

When implementing communication by use of the subsets explained above,it can be carried out by replacing the subcarriers shown in the otherembodiment with subsets. Namely, subcarriers f1-f7 shown in FIGS. 3, 6,7, 8, 12, 15, 17, 18 and 20-24 may be replaced with subsets. Meanwhile,where a plurality of subcarriers are assigned to one subset, it ispossible to carry out such an operation as direct sequence by use of aparticular subcarrier or frequency hopping by use of a subcarrierassigned within the relevant subset.

FIGS. 29 and 30 shows a frequency hopping pattern where subsets areconstituted as shown in FIG. 27. FIG. 29 is the case where thecommunication apparatus performs transmission through one channel byusing all the subsets while FIG. 30 is the case where three channelsperform transmissions each using one subset. In this manner, by controlof communication through two-stages of divisions with subsets andsubcarriers, it is possible to control subsets and subcarriers nearly onthe same control scheme. Thus, a high-function communication system canbe architected by a simple configuration.

In this manner, by putting together a plurality of subcarrier as asubset and thereby carrying out communication control independentlybased on the subset or carrying out communication control by acombination of subsets and subcarriers, a simple and efficientcommunication system can be architected as compared to control ofsubcarrier entirety.

Embodiment 9

The present embodiment explains an invention for detecting an output ofa broadband signal by a simple configuration.

FIG. 3 shows an on-frequency allocation of a broadband signal to bedetected and detecting subcarrier signals. In the figure, the broadbandsignal is shown by a dotted line and the subcarrier signals by hatchingof f1-f7. The broadband signal and the subcarrier signals have afrequency relationship set such that the entire or a part band of thesubcarriers is positioned within a band of the broadband signal, asshown in FIG. 3.

FIG. 38 shows one example of an arrangement of a reception apparatus tobe used in the invention. Note that the constituent element having likefunction in the figure is attached with like reference. The receptionapparatus comprises a reception section 202 for decomposing a broadbandsignal into a plurality of subcarrier signals f1-fn (narrow in band ascompared to that) and receiving the decomposed signal group, and adetermining section 3801 for inputting the received reception signalgroup and outputting a determination result. The determination section3801 comprises a compensation section 401 for inputting the receivedreception signal group and compensating for any of amplitude, phase,delay time and waveform of each signal, and a detection section 3802 forinputting a compensated signal and outputting a desired signal.

The operation is explained in the below by using the figures.

At first, the broadband signal is divided into signals (subcarriersignals) divided in predetermined bands by a filter (not shown), andinputted to the reception apparatus. In the compensation section 401,the inputted subcarrier signals are compensated for in a manner easy todetect a phase, an amplitude, a delay time, a waveform, etc. As shown inFIG. 39, the subcarrier signals separated from the same broadband signalare sought as signals high in time correlation depending upon thecorresponding frequency characteristics. By a filter characteristic orpropagation path characteristic used in separation, variation occurs inamplitude, phase, delay time, waveform, etc. In the figure, there areshown an actual signal and an ideal waveform respectively by a solidline and a dotted line. By taking subcarrier f2 as a reference,subcarrier f1 is long in delay time and great in amplitude. Conversely,subcarrier f3 is short in delay time and small in amplitude, whereinamplitude is inverted. In this manner, because the subcarrier signalsvaries depending upon a propagation characteristic and filtercharacteristic, a difference occurs in detection characteristicdepending upon a communication condition and a combination of filters.

In order to solve the problem, the compensation section 401 makes acompensation into a signal matched in amplitude, phase, delay time andwaveform. Namely, compensation is performed in a manner approximate tothe dotted line shown in FIG. 39. In the figure, although subcarrier f1longer in delay time is matched to subcarrier f2 shorter in delay time,delay time is desirably matched to the longest one if considering a factthat the delay element is easier to control. By compensation as above,the subcarrier signals are outputted as signals matched in amplitude,phase, delay time and waveform, as shown in the dotted line in FIG. 39.

Next, in the signal detection section, it is determined whether acommunication signal has been received or not, by a detection time of animpulse equal to or greater than a constant level of among thesubcarrier signal group and the number thereof. Namely, in the case of asimultaneous (within a set time difference) impulse detection out of apredetermined number of subcarrier signals, determination is made asreceiving a broadband signal.

In the case that another communication signal is narrower in band ascompared with a broadband signal to be detected by the presentapparatus, even in case signal power is detected on any of subcarriersignals, there is no case that signal power is detected on all thesubcarrier signals. Consequently, even in case another communicationsignal interferes with a particular subcarrier to thereby detect animpulsive signal, the affection thereof can be removed unless there areinterferences with a constant number or more of subcarriers.

Generally, when to detect a broadband signal, the broadband signal isvery frequent in signal change and hence very high-speed of operation isrequired to follow the same. Meanwhile, because the communicationterminal before communication start is not prepared for time synchronismand system synchronism (synchronism in hopping), the prior art requiresoperations including synchronization and demodulation in order to carryout only signal power detection. In such a situation, although signaldetection is made by using correlation operation at a constant timeinterval. However, correlation operation is complicated in operation,thus having a great problem in respect of circuit scale and powerconsumption leading to signal processing complication and consumptionpower increase. Particularly, because the communication signal detectingoperation as in the foregoing is a function required in waiting for areception, there is a problem that restriction is provided in receptionwait time. Generally, reception wait time occupies a great ratio ascompared to the time executing communication. Naturally, there is nooperation of a function as a communication during waiting for areception. Consequently, there is also a problem of quite worseconsumption efficiency in a total viewpoint.

These problems are attributable to the impossibility for thecommunication apparatus to distinguish a signal affected by aninterference with other systems. The present invention aims at resolvingsuch a problem. Namely, when detecting a broadband signal as compared tothe band which the general communication system utilizes, the influenceof an interference signal is restricted by dividing it in frequency. Bysuch division into some narrow-band subcarriers and detecting acommunication signal on the basis of a signal power obtained from thesubcarriers, it is possible to configure a communication signaldetection apparatus extremely simple and low in consumption power.

The detection signal thus determined is representative of a time ofcommunication signal, and hence can be used as the initial synchronoussignal with the subsequent signal. By doing so, a communicationapparatus can be architected that is simple and low in consumptionpower.

Meanwhile, as a determination criterion, an operation result of additionof signal groups can be taken as a reference signal. Namely, determinedis a signal that all the subcarrier signals are added and synthesizedtogether. In the case the power value of the same exceeds a constantlevel, detection determination is carried out. Otherwise, with referenceto a time the power value exceeds a constant level, in the case ofdetecting an impulse by a constant number of subcarriers within aconstant time at around the same, detection determination is done. Bydoing so, operation is made possible at extremely low consumption powerbecause the operation prior to signal detection is limited to reception,operation and power detection.

INDUSTRIAL APPLICABILITY

As in the above, the present invention is useful in electronic commercetransaction with utilization of a program broadcast with advertisementdistribution, and suited for prompting the viewer to look anadvertisement, carrying out sales promotion without discount of theadvertisement product and extending the demand for pay broadcast.

LIST OF REFERENCES IN DRAWINGS

-   101 ANTENNA-   102, 2501 RECEPTION DEMODULATION PART-   103 TRANSMISSION MODULATION PART-   150 TRANSMISSION APPARATUS-   151 RECEPTION APPARATUS-   201 FILTER-   202 RECEPTION PART-   203 DEMODULATION PART-   204 MODULATION PART-   205 TRANSMISSION PART-   206, 502 WAVEFORM GENERATING PART-   250 FILTER PART-   401, 501 COMPENSATION PART-   402 OPERATION PART-   403 DETECTION PART-   901 SPREAD CODE STORING PART-   902 DISPREAD PART-   903, 1002 MULTIPLICATION PART-   1001 SPREAD PART-   1950, 1951 COMMUNICATION APPARATUS-   2501 SWITCH PART-   2503 CARRIER CONTROL PART-   3101 FREQUENCY CONVERSION PART-   3801 DETERMINING PART-   3802 DETECTION PART-   4001 CHANNEL CONTROL PART-   4401 SUBCARRIER GENERATOR & MODULATOR-   4402 SUBCARRIER TIME MODULATOR-   4403 OUTPUT STAGE-   4404 ANTENNA

1. A communication apparatus comprising: a transmission modulator forimpulse modulating transmission data into subcarrier modulation signalsusing a plurality of subcarriers; a transmission part for generating aplurality of subcarrier-transmission signals by amplifying the pluralityof subcarrier modulation signals; a filter section for filtering theplurality of subcarrier-transmission signals, thesubcarrier-transmission signals being band-limited within a bandwidthallocated for each of the subcarriers the subcarrier transmissionsignals having a cumulative bandwidth narrower than a bandwidth of thesubcarrier modulation signals; a carrier control section for controllingthe subcarriers for use in communication depending upon informationamount, significance and communication propagation condition; and anantenna section for multiplexing and radiating the filtered subcarriertransmission signals.
 2. A communication apparatus according to claim 1,further comprising a reception modulator for detecting reception dataand examining a reception power on each subcarrier, to notify to thesubcarrier control section a permission/non-permission to use thesubcarrier, depending upon the reception power examined by the receptiondemodulator.
 3. A communication apparatus according to claim 2, whereinthe carrier control section causes hopping two or more of thesubcarriers.
 4. A communication apparatus according to claim 2, whereinthe carrier control section causes spread on two or more of thesubcarriers.
 5. A communication apparatus according to claim 1, whereinthe transmission modulator changes an on-frequency allocation of thesubcarriers according to communication condition.
 6. A communicationapparatus according to claim 1, wherein the transmission modulatorassigns a narrower band to the subcarrier having a lower centerfrequency and a broader band to the subcarrier having a higher centerfrequency.
 7. A communication apparatus according to claim 1, furthercomprising a channel control section for selecting and controlling thesubcarrier for use on each channel, the channel control sectionperforming communication over two or more channels with different onesof the subcarriers.
 8. A communication apparatus according to claim 7,wherein the channel control section performs communication over two ormore channels with a combination of different ones of the subcarriers.9. A communication apparatus according to claim 1, wherein carriercontrol section performs communication of control information by atleast one of the subcarriers.
 10. A communication apparatus according toclaim 9, wherein the transmission modulator multiplexes together thepieces of control information on two or more channels by use of any oneof time division multiplexing and code division multiplexing, in atleast one subcarrier of two or more of the subcarriers.
 11. Acommunication apparatus according to claim 2, wherein the transmissionmodulator carries out frequency division duplex by use of two or more ofthe subcarriers.
 12. A communication apparatus according to claim 9,wherein the transmission modulator carries out frequency division duplexby use of three or more of the subcarriers.
 13. A communicationapparatus according to claim 9, wherein the subcarrier with which thetransmission modulator is to communicate the control information has acenter frequency lower than a center frequency of the other subcarrier.14. A communication apparatus according to claim 9, wherein thesubcarrier with which the transmission modulator is to communicate thecontrol information has a band narrower than a band of the othersubcarrier.
 15. A communication apparatus according to claim 7, whereinthe modulation part divides one symbol into two or more of thesubcarriers, thereby multiplexing two or more channels.
 16. Acommunication apparatus according to claim 15, wherein the transmissionmodulator causes frequency hopping in one symbol by use of two or moreof the subcarriers, to thereby multiplexing two or more channels.
 17. Acommunication apparatus according to claim 15, wherein the transmissionmodulator causes encoded spread of one symbol onto two or more of thesubcarriers, to thereby multiplexing two or more channels.
 18. Acommunication apparatus according to claim 15, wherein the transmissionmodulator causes spread of one symbol onto two or more of thesubcarriers and two or more chips, thereby multiplexing two or morechannels.
 19. A communication apparatus according to claim 1, whereinthe antenna section comprises a plurality of antenna elements.
 20. Acommunication apparatus according to claim 1, wherein the antennasection has a frequency characteristic of a multi-band characteristic.21. A communication apparatus according to claim 19, wherein the antennaelements are different in center frequency of frequency characteristic.22. A communication apparatus according to claim 21, wherein the antennaelements have band characteristics not to overlap on a frequency axis.23. A communication apparatus according to claim 2, wherein the antennasection receives radio wave on a subcarrier-by-subcarrier basis andoutputs the subcarrier signal to the reception modulator.
 24. Acommunication apparatus according to claim 19, wherein the antennaelements have frequency characteristics corresponding to the subcarriersand radiate subcarrier transmission signal as a radio wave.
 25. Acommunication apparatus according to claim 2, wherein the receptiondemodulator has a compensation section for detecting a characteristic ofa signal sequence of each subcarrier from a known signal received from acommunication partner and compensating for the characteristic.
 26. Acommunication apparatus according to claim 25, wherein thecharacteristic is a frequency characteristic.
 27. A communicationapparatus according to claim 25, wherein the characteristic is a timeresponse characteristic, the compensation section compensates the timeresponse characteristic by a correlation signal of a correlator.
 28. Acommunication apparatus according to claim 2, wherein the receptiondemodulator comprises a spread code storing section for storing a spreadcode and extracting a spread code corresponding to the subcarrier, and adispread section for making a convolution operation of the subcarriersignal and the spread code extracted at the spread code storing section.29. A communication apparatus according to claim 1, wherein thetransmission demodulator comprises a spread code storing section forstoring a spread code and extracting a spread code corresponding to thesubcarrier, and a spread section for making a direct spread onto thesubcarrier from the modulation signal divided into the subcarriers andthe spread code extracted at the spread code storing section.
 30. Acommunication apparatus according to claim 2, wherein the receptiondemodulator comprises a switch section for switching over by frequencyhopping on the subcarrier, the carrier control section carrying out thecontrol in the switch section.
 31. A communication apparatus accordingto claim 1, wherein the transmission demodulator comprises a switchsection for switching over by frequency hopping on the subcarrier, thecarrier control section carrying out the control in the switch section.32. A communication apparatus according to claim 1, further comprising acarrier control section for controlling the subcarriers for use incommunication depending upon information amount, significance andcommunication propagation condition.
 33. A communication methodcomprising the steps of: impulse modulating transmission data intosubcarrier modulation signals using a plurality of subcarriers;generating a plurality of subcarriers transmission signals by amplifyingthe plurality of subcarrier modulation signals; and filtering thesubcarrier transmission signals, the subcarrier transmission signalsbeing band limited within a bandwidth allocated for each of thesubcarriers, the subcarrier transmission signals having a cumulativebandwidth narrower than a bandwidth of the subcarrier modulation signalstransmitting, by an antenna, the filtered subcarrier transmissionsignals, and measuring a reception power on each of the subcarriers in anon-signal state, in an initial state prior to starting a communication;and determining the reception power measured and selecting thesubcarrier usable in communication.
 34. A communication method accordingto claim 33, wherein the determination is to use, in a latercommunication, the subcarrier having the reception power equal to orsmaller than a predetermined value.
 35. A communication method accordingto claim 33, further comprising a step of measuring a reception power onevery subcarrier of a received known signal at a start of communication;and a step of selecting the subcarrier having the measured receptionpower equal to or greater than a predetermined value, as a subcarrierusable in communication.